Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.61	4.245%	$19.4	$19.40	$19.40	$19.40
Purchase #2	$209.39	4.874%	$219.5957	$219.60	$219.60	$219.60
Purchase #3	$15.89	5.620%	$16.783	$16.78	$16.80	$16.80
Purchase #4	$80.31	6.558%	$85.5767	$85.58	$85.60	$85.60
Purchase #5	$246.97	11.697%	$275.8581	$275.86	$275.85	$275.90
Purchase #6	$221.89	3.251%	$229.1036	$229.10	$229.10	$229.10
Purchase #7	$30.66	9.371%	$33.5331	$33.53	$33.55	$33.50
7 purchase totals =	$823.72		$879.8502	$879.85	$879.90	$879.90